UIView Extension #6
func animateBG2Black(duration:CGFloat=0.3){
    UIView.setAnimationBeginsFromCurrentState(true)
    UIView.animateWithDuration(NSTimeInterval(duration), delay: 0.0, usingSpringWithDamping: 1.0, initialSpringVelocity: 0.0, options: UIViewAnimationOptions.CurveLinear,
        animations: { () -> Void in
            self.backgroundColor = UIColor.blackColor()
        },
        completion: { (finish:Bool) -> Void in
            
        }
    )
}